It's akin to muscle memory I presume, but once you've seen a couple of the angles held in position, and the pattern emerge on whatever the edge is it makes it easier to do without the guide. A light touch to the wheel and have a look to see where the grid is helps too. Adjust the angle you're contacting at accordingly and away you go, touch at a time.I've got a drill sharpening bit of paper explanation, pinned up next to the bench grinder at work.
I've tried free hand, but little success, a guide would probably / undoubtedly help, the small drills at work are expendable, but 10 to 20mm, be good if we could resharpen them.
I do form tools and boring bars with an angle grinder, it takes material off so much faster, and you can hold it in a vice rather than burn your fingers. Of course I then clean it up on a bench grinder, and finish it with a stone.
You can do very well with drill bits just by marking the tip angle on the rest with a sharpie.